Single-stage single-switch PFC converter with extreme step-down voltage conversion ratio

This paper presents a new single-stage singleswitch (S⁴) high power factor correction (PFC) AC/DC converter suitable for low power applications (< 150 W) with a universal input voltage range (90-265 V_rms). The proposed topology integrates a buck-boost input current shaper followed by a buck and a buck-boost converter, respectively. As a result, the proposed converter can operate with larger duty cycles compared to the exiting S⁴ topologies; hence, making them suitable for extreme step-down voltage conversion applications. Several desirable features are gained when the three integrated converter cells operate in discontinuous conduction mode (DCM). These features include low semiconductor voltage stress, zero-current switch at turn-on, and simple control with a fast well-regulated output voltage. A detailed circuit analysis is performed to derive the design equations. The theoretical analysis and effectiveness of the proposed approach are confirmed by experimental results obtained from a 35-W/12-V_dc laboratory prototype.